A run flat tire is required to have an ability to run continuously for a relatively long distance at a high speed under a deflated or punctured condition. For example, to achieve safe running on expressways, a run flat tire is required to have such an ability to run for a distance of more than 50 km at a speed of about 80 km/hr.
Hitherto, a system in which a load supporting elastic member is disposed inside a tire, and a system in which an inflated tube member like a small size tire is separately disposed inside a tire to form a double-chamber structure, have been proposed. Such systems, however, do not serviceability because of the increased weight and the resultant decrease in dynamic characteristics as well as further complex maintenance works.
Therefore, to increase the sidewall thickness and thereby to support the tire load under deflated conditions, a tire in which a reinforcing rubber layer is disposed on the axially inside of the carcass in each of the sidewall portion, has been proposed. However, when the sidewall thickness is simply increased, the tire weight is also increased; and radiation of internal heat is hindered which results in an internal structural failure; and further ride comfort is impaired. On the other hand, to avoid the thickness increase, when the elastic modulus of the rubber against a compressive stress is increased, the tire is durability against the repeated bent deformation is lost, and further heat generation increases.